The present invention relates to power factor correction (PFC) converters, and more particularly to interleaved PFC converters.
Electric power is distributed almost universally in an alternating current (AC) format that allows for efficient transmission. Most devices however, including personal computers, televisions, etc., require direct current (DC) power. Power supplies act to convert the AC input supplied by a line to a DC output suitable for consumption by a device or load or act to convert a DC input to a DC output (i.e., a DC-to-DC converter). A switched-mode power supply (SMPS) employing a boost regulator is commonly employed in this role of AC-to-DC or DC-to-DC power conversion. A benefit of employing a SMPS having a boost regulator topology is the boost regulator can be controlled to provide power factor correction. Subsequent stages may be employed to step-down the output of the PFC boost regulator to a desired DC output voltage.
A boost regulator includes an inductor connected between a rectified input and the DC output. A shunt switch is selectively controlled to charge the inductor (during ON times of the switch) and to discharge the inductor to the DC output (during OFF times of the switch). The power capability of a converter may be increased (or alternatively, the size of the converter decreased) by connecting PFC boost regulators in parallel with one another and controlling them in an interleaved manner to provide the desired output. In a discontinuous conduction mode (DCM), each inductor must be completely discharged before the switch associated with the inductor is turned ON. If the discharge cycle is not complete (i.e., current through the inductor at the beginning of the charging cycle is non-zero), the converter operates in a continuous conduction mode (CCM) that is detrimental to control of the output voltage. Efficient operation of the PFC boost regulators therefore requires accurate monitoring of the current through each inductor. Prior art methods monitor the current through each inductor directly using either an auxiliary winding or transformer associated with each inductor. However, this requires additional and larger hardware, thereby increasing the size and cost of the device.